Absolutely Confabulous

Confabulation is a striking symptom of some kinds of brain damage. Patients tell often fantastic stories about things that have happened to them, or that are going on now. It's a classic sign of Korsakoff's syndrome, a disorder caused by vitamin B1 deficiency due to chronic alcoholism.

Korsakoff's was memorably illustrated on House (Season 1 Episode 10, to be exact). Here's a clip; unfortunately, it's overdubbed in Russian, but you can hear the original if you pay attention.

Why does confabulation happen? An influential theory is that confabulation is caused by a failure to filter out irrelevant memories. Suppose I ask you to tell me what happened yesterday. As you reply, yesterday's memories will probably trigger all kinds of associations with other memories, but you'll able to recognize those as irrelevant: that wasn't yesterday, that was last week.

A confabulating patient can't do that, this theory says, so they end up with a huge jumble of memories; the confabulated stories are an attempt to make some sense of this mess. See above for my attempt to confabulate a story linking the three random concepts of a cat, a fire engine and a chair.

Now British neuroscientists Turner, Cipolotti and Shallice argue that this is only part of the truth: Spontaneous confabulation, temporal context confusion and reality monitoring. They discuss three patients, all of whom began to confabulate after suffering ruptured aneurysms of the anterior communicating artery, which destroyed parts of their ventromedial prefrontal cortex.

The patient's stories are tragic, although we can take solace in the fact that they presumably don't know that. The confabulations ranged from the mildly odd:

Patient HS was a 59-year-old man admitted after being found disoriented in the street. [he] had undergone clipping of an ACoA aneurysm 25 years previously. He had been left with a profound confusional state, memory impairment, and confabulation. As a result, HS had been unable to return to work and had spent at least part of the intervening period homeless...

He... continued to produce spontaneous confabulations involving temporal distortions (believing that he had undergone surgery only 18 months previously) and other source memory distortions (confusing memories of interactions with the examiner with interactions with other patients).

To the surreal:

GN was disoriented to place, situation, and time and produced consistent confabulations, for example, believing that the year was 1972 and that he was in a hospital in America after being shot. He regularly produced markedly bizarre confabulations, for example, reporting that he had attended a party the night before and met a woman with a bee’s head. He frequently attempted
to act upon his mistaken beliefs, for example, attempting to leave the hospital to attend meetings.

Anyway, in order to try to discover the mechanism of confabulation, they gave the patients some memory tests. The results were clear: the confabulating patients had no problems remembering stuff, but were unable to tell where they remembered it from.

For example, in one task, the subjects were shown a series of pictures, some of which appeared only once, and some of which were repeated. They had to say which ones were repeats.

The patients did normally the first time they did this task, but when they did the test again, this time with a different subset of pictures repeated, they ran into problems, saying pictures that appeared only once during the session were repeats. They were unable to tell the difference between repeats within the session and repeats from previous sessions. This replicates an earlier study of other confabulators.

But Turner et al found that this lack of awareness for the source of information, wasn't just limited to when things happened. The confabulating patients were also unable to tell the difference between things they'd actually heard, and things they'd only imagined.

Subjects were read a list of 15 words, and also told to silently imagine 15 other words (e.g. "imagine a fruit beginning with A" - apple). They were later asked to remember the words and to say whether they were heard or just imagined. Patients did well on the task except that they wrongly said that they'd actually heard many of the imagined words.

The authors conclude that confabulation is caused by a failure to recognize the source of memories, not just in terms of time, but in terms of whether they were real or fantasy. For a confabulator, all memories are of equal importance. Why this happens as a result of damage to certain parts of the brain remains, however, a mystery.

Turner MS, Cipolotti L, & Shallice T (2010). Spontaneous confabulation, temporal context confusion and reality monitoring: A study of three patients with anterior communicating artery aneurysms. Journal of the International Neuropsychological Society : JINS, 1-11 PMID: 20961471